1. Field of the Invention
The present invention relates to mass spectrometers, and more particularly to a tandem mass spectrometer in which a time-of-flight mass spectrometer is combined with a mass spectrometer such as a quadrupole mass spectrometer and an ion trap mass spectrometer.
2. Description of the Related Art
A mass spectrometer ionizes molecules to be measured, and emits the ionized molecules to an electric field/a magnetic field. Then, the mass spectrometer uses the difference in flight course based on the mass number/ionic valence to determine a mass-to-charge ratio (m/z), and thereby to identify a kind of molecules to be measured. As a method for detecting the difference in flight course, there are a method for determining how a flight course is curved (quadrupole mass spectrometer), a method for measuring a difference in flight time (time-of-flight mass spectrometer), and the like. In order to improve the analysis precision/efficiency, a method in which molecules to be measured are selected on a molecular weight basis using a column in front of a mass spectrometer (liquid chromatography, gas chromatography) is used in combination with the above methods. In order to further select molecules to be measured, a quadrupole mass spectrometer or an ion trap mass spectrometer is also often located in front of the mass spectrometer so that the molecules which have been selected by the chromatography fall within a range of a specific mass-to-charge ratio. To be more specific, by applying a constant high-frequency current between electrodes of the quadrupole mass spectrometer, which are opposed to each other, or between ring and end-cap electrodes of an ion trap, it is possible to accumulate ions in the electrodes. Moreover, by applying an assistant high-frequency current having specific frequency/voltage, only ions which fall within a specific mass-to-charge ratio can be kept remained in the electrodes. A method for improving the precision/efficiency of the mass spectrometry in this manner is disclosed in, for example, Patent Document 1 (JP-A-2005-108578).